Electricity is transmitted from generating stations to electrically-powered devices by metal conductors. The preferred metal is copper because of its excellent conductivity and relatively low price. The metal conductors are known as wires when they consist of relatively small diameter single strands and are known as cables when they consist of multiple strands wound together. Both wire and cable are commonly coated with a flexible plastic insulator. Most electrically-powered devices are connected with at least three separate wires or cables, one is known as the positive, one is known as the negative or neutral, and one is a ground cable whose purpose is to carry the current to the Earth in the event of a malfunction.
On an atomic level, the flow of electricity is the movement of electrons. The movement generates friction and the friction generates heat. The diameter of the conductor must be large enough to prevent the generation of excessive heat. The minimum safe diameter of the conductor is thus a function of the voltage and current of the electricity. For example, 12 gauge (American wire gauge) copper wiring having a diameter of about 0.08 inches (about 3.2 mm) is used for many residential circuits (120 volts and 20 amperes) whereas copper cable for industrial use is often one inch (about 2.5 cm) or more in diameter.
For residential and commercial buildings, three or four insulated wires preformed within a flexible plastic sheath are commonly used for the electrical system. For industrial applications, the wires or cables are usually placed within a rigid enclosure made of metal or hard plastic at the installation site. The enclosures are commonly known as conduits when they have a round cross section and are commonly known as raceways when they have a rectangular cross section. The term “conduit” is used herein to refer to any type of rigid enclosure for wires and cables. The conduit provides additional protection and safety for the wires and cables. The installation process requires the wires and cables to be pulled through the conduit.
Pulling large diameter cables through a conduit is difficult because the cables tend to bind with each other and to rub against the inside wall of the conduit. While pulling through a straight conduit can be difficult, pulling through curved sections of conduit is even more difficult. Electricians commonly coat the cables with a solution of soapy water or other lubricant to reduce friction as they are pulled through a conduit.
A variety of conduit inserts have been disclosed. For example, Conti et al., U.S. Pat. No. 5,027,864, Jul. 2, 1991; Allen, U.S. Pat. No. 6,262,371, Jul. 17, 2001; Washburn, U.S. Pat. Appln. Publn. No. 2007/0130760, Jun. 14, 2007; and Morris, U.S. Pat. No. 7,319,802, Jan. 15, 2008, disclose conduit inserts that run the entire length of the conduit and separate individual cables within the conduit. These conduit inserts require the cables to be fed simultaneously into the inserts. It is very difficult to precisely align and then feed three or more bulky cables simultaneously into a conduit insert.
A variety of cable supports and protectors have also been disclosed. For example, Henry, U.S. Pat. No. D436,578, Jan. 23, 2001; Wakamatsu, U.S. Pat. No. 5,780,773, Jul. 14, 1998; Ayoub, U.S. Pat. No. 7,633,010, Dec. 15, 2009; and Symons, U.S. Pat. No. D648,685, Nov. 15, 2011, disclose cable supports and protectors that separate cables. However, these cable supports and protectors are not suitable for use in conduits.
Accordingly, there is a demand for an improved cable guide that enables multiple cables to be separated in a conduit at desired intervals and that can be placed onto the cables without requiring the cables to be fed into and through the guide.